Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.44   8.765%   $94.0165   $94.02   $94.00   $94.00  
  Purchase #2 $98.84   10.207%   $108.9286   $108.93   $108.95   $108.90  
  Purchase #3 $208.58   7.747%   $224.7387   $224.74   $224.75   $224.70  
  Purchase #4 $203.28   9.331%   $222.2481   $222.25   $222.25   $222.20  
  Purchase #5 $49.48   7.191%   $53.0381   $53.04   $53.05   $53.00  
  Purchase #6 $122.42   13.804%   $139.3189   $139.32   $139.30   $139.30  
  Purchase #7 $200.85   3.757%   $208.3959   $208.40   $208.40   $208.40  
  7 purchase totals = $969.89       $1,050.6848   $1,050.70   $1,050.70   $1,050.50